1. Field of the Invention
The present invention is directed to refillable bulk liquid canisters, and in particular, to methods, systems and apparatus for automatically controlling and maintaining a pressure differential between supply canisters and receiving canisters within a bulk delivery assembly for continuous delivery of a liquid chemical to manufacturing process tools
2. Description of Related Art
In the manufacture of semiconductor devices, chemical vapor deposition (CVD) techniques are often used to deposit various layers onto a substrate. The liquid chemicals (hereinafter “liquid”) used by the CVD tools are received at the CVD processing tools via bulk feeding from a remote bulk delivery cabinet. Various remote delivery cabinets exist in the art including, for example, those that bubble a liquid from a canister to the processing tools, or those that push a liquid along a path running from a refillable bulk supply source to a process canister and out to the processing tools. Since liquid bubbling cabinets are limited to the amount of liquid residing with the bubbled canister, these systems are generally not as extendable to the various processing techniques in the art as compared to those systems having a supply source of liquid for continued supply.
Refillable bulk liquid delivery cabinets include a bulk canister in combination with a process canister. The bulk canister retains the liquid (e.g., liquid precursors, such as, TEOS), and when it is determined that the liquid within the process canister falls below a preset level, the bulk canister delivers and refills the process canister with enough liquid to satisfy the preset level. The process canister pushes this liquid to the manufacturing equipment (e.g., the CVD tool). A delivery system that includes the bulk and process canisters alone is generally beneficial when the manufacturing equipment consumes small quantities of liquid chemicals, such as, for example, thin film depositions.
However, when the manufacturing equipment consumes large quantities of liquid chemicals, it is often necessary that the liquid chemical delivery equipment also include bulk canisters that can supply this demand. One approach in the prior art is to replace the bulk canister while the process canister continues to run. In so doing, the bulk canister is taken offline while the process canister continues to supply the chemical. This approach is undesirable since the liquid in the process canister can quickly deplete while the bulk canister is off-line, leading to manufacturing interruptions, which in turn, often result in time delays, decreased production yields and increased costs.
Another approach for providing large quantities of liquids is to provide the bulk delivery system with a large central supply canister that can supply multiple bulk canisters located at source cabinets for the production equipment. Such a configuration may include a 200 Liter central supply canister within a secondary cabinet that fills the bulk canister(s) at the source cabinets. The use of a larger central supply canister eliminates the need to take production equipment off line, thereby reducing the number of container changes, labor, and shipping costs.
In order for bulk delivery systems having a large central supply canister(s) to work properly, it is necessary that the pressures within the central supply canister, each bulk canister and each process canister be continuously maintained for continued flow of the liquid to the processing tools. The flow path is ideally a hierarchial flow path output from the central supply canister, to the bulk canister(s), to the process canister(s), and then out to the processing equipment. Along this flow path, a Delta pressure must be maintained such that the central supply canister has a higher pressure than the bulk canister(s) it supplies liquid to, and in turn, the bulk canister(s) has a higher pressure than the process canister(s) to which it supplies such liquid for proper functioning of the bulk delivery system.
Currently, pressures within such bulk delivery systems are regulated through the use of manually preset pressure regulators, which are programmed to a desired set point delivery pressure. Each canister within the system may be provided with one of these manually preset pressure regulators. However, manually preset pressure regulators only determine if the pressure within a given canister falls below (or under) the programmed set point, and if so, the pressure within such canister is increased through the use of a pneumatic valve for adding Helium to the canister. These manually preset pressure regulators do not take into account over pressures within the canisters of the bulk delivery system.
Another deficiency of the manually preset pressure regulators is that they have a five percent fluctuation range from the preset desired set point delivery pressure. This means that the pressure for a given canister can undesirably drift five percent above or below its desired pressure set point. A five percent drift below the desired pressure set point may slow the liquid flow path, which can undesirably slow production and decrease production yields. Similarly, a five percent drift above the desired pressure set point may increase the liquid flow path to undesirably result in a thicker than desired layer deposition, which may also decrease production yields. The five percent pressure fluctuation of these manually preset pressure regulators may further interfere with the Delta pressure between the large supply canister, supply canister(s) and process canister(s), causing a potential equilibrium therebetween, such that, the liquid flow stops within the delivery system (i.e., the liquid is not pushed along the flow path), thereby also slowing production and decreasing production yields.
While prior art is directed to pressure and flow regulators on the output of the regulator to control the flow of push gas pressure into other source canisters based on under pressure conditions, the prior art does not take into account over pressure conditions as a result of the pressure of the liquid being supplied or any variations from the regulator settings. Currently, to recover from a pressure imbalance due to over pressure conditions, an operator must wait for such an event to occur, and then manually vent off the helium supply pressure to regulate the pressure back down to the desired set point delivery pressure.
Accordingly, there is a need in the art for methods, systems and apparatus that automatically take into account both under and over pressure imbalances within a liquid bulk delivery system for the uninterrupted stream of liquid chemicals to multiple process tools.